Among in-cylinder injection type internal combustion engines that inject fuel directly into combustion chambers to produce an air-fuel mixture, which are so-called direct-injection engines, there are ones that produce a stratified air-fuel mixture in combustion chambers by spray-guide method in order to carry out a lean-burn operation at part load.
These engines that produce a stratified air-fuel mixture, as disclosed for example in Unexamined Japanese Patent Publication No. 10-54246, include an engine that has a combustion chamber provided in its wall with an injection part of a fuel injection valve and an ignition part of a spark plug which are arranged alongside, and injects fuel from the injection part directly to the vicinity of the ignition part of the spark plug to secure an air-fuel mixture area having a theoretical air-fuel ratio suitable for ignition in the vicinity of the spark plug, while putting the whole combustion chamber into an excess-air condition. During part-load operation, lean burn is performed in the combustion chamber, using as a source of ignition a relatively rich air-fuel mixture area that is created near the ignition part of the spark plug.
In order to produce the air-fuel mixture suitable for ignition near the ignition part in the engine that produces the stratified air-fuel mixture, it is required to set the spark plug as close as possible to the injection part of the fuel injection valve but separately enough to prevent a blow-off of electric discharge which is caused by a high gas flow velocity during the fuel injection so that the fuel injected from the fuel injection part of the fuel injection valve may be injected to a target position near the ignition part.
However, since the spark plug is located close to the fuel injection valve, the flow velocity of the fuel injected from the fuel injection valve is high. The air-fuel mixture suitable for ignition therefore remains in the vicinity of the ignition part of the spark plug only for a short time.
Because the ignition has to be completed for this short time, an operation range that enables stable combustion is narrow during the lean-burn operation.
To solve the above problem, a lean burn engine using a spray-guide method has been proposed, in which fuel is caused to strike against an obstacle before the ignition part so that the fuel bounced off the obstacle is fed to the vicinity of the ignition part of the spark plug, for example, as disclosed in Unexamined Japanese Patent Publication No. 2006-291798, instead of feeding the fuel directly to the ignition part of the spark plug as described above.